Production of aqueous or anhydrous hydrogen chloride free of sulfur dioxide



3,492,091 CHLORIDE Jan. 27, 1970 l T. M. GOLDMAN ETAL V PRODUCTION 0F AQUEOUS OR ANHYDROUS HYDROGEN FREE OF SULFURKDIOXIDE Filed Aug. 2, 1967 moEw wm Sanoma United States Patent 3,492,091 PRODUCTION 0F AQUEOUS 0R ANHYDROUS HYDROGEN CHLORIDE FREE OF SULFUR DIOXIDE Thomas Milton Goldman and Robert Lamar Jordan,

Fort Worth, Tex., assignors to Stauffer Chemical Company, New York, N Y., a corporation of Delaware Filed Aug. 2, 1967, Ser. No. 657,979 Int. Cl. C01b 7/08 U.S. Cl. 23-154 4 Claims ABSTRACT OF THE DISCLOSURE An aqueous liquor containing HC1 and S02 is treated with elemental chlorine, applied in stoichiometrical excess with respect to the SO2 to oxidize the latter to H2804. Following separation of the H2804, the HCl product is treated to remove the excess chlorine.

This invention relates to a method for producing essentially sulfur-free aqueous and anhydrous hydrogen chloride.

The invention is particularly concerned with, but not limited to, the processing of HC1 as derived from a Mannheim furnace. Such a furnace is normally fired with natural gas and is employed to achieve the reaction:

Incident to the reaction, some sulfur dioxide is also produced. As a consequence, the nal HC1 product whether aqueous or anhydrous, normally contains an appreciable amount of 802 as a contaminate. In many applications the 802 is acceptable, but in other areas even minute quantities are considered highly objectional. This is so, for example, among users of HC1 for oil well acidizing. Also, there have been objections to the conventional anhydrous product from the electronic industry where anhydrous HC1 is commonly used in etching of silicone insulating wafers.

Accordingly, the invention has as a principal object to provide a process whereby the 802 content of the HCl, whether aqueous or anhydrous, is reduced to a point rendering the product fully acceptable in the indicated areas of use.

A further object is to achieve such goal at minimal cost.

Still other objects and features of the invention will become apparent from the further description which will proceed with reference to the accompanying drawing diagrammatically illustrating a system adapted for the practice of the invention.

Although the particular system shown is designed to be integrated with, or interposed in, an existing assemblage of equipment adapted for the processing of vapors derived from a Mannheim furnace, its application is not to be taken as so restricted. However, a brief description of the processing which proceeds upstream of the illustrated system is believed in order. Suffice it to say, that the vapor effluent of the furnace is first subjected to adiabatic humidication with water and aqueous HCl to reduce the temperature thereof. Thereafter the vapors are scrubbed with weak aqueous HCl to remove entrained dust, consisting in the main of K2S04 lines, and then absorbed in water which is conveyed to a surge tank along with the bottom product of the scrubbing unit.

In accordance with the invention (see drawing), the liquid from the surge tank 9, analyzing typically as indicated on the drawing, is fed to a stripper in company with elemental chlorine (tank 11) applied in an amount greater than that required to oxidize the S02 to sulfuric acid in accordance with the equation:

3,492,091 Patented Jan. 27, 1970 The bottom product of the stripper 10 consisting typically of 17 percent HC1, 10 percent H2804 and 73 percent H20 is applied in the scrubbing operation aforementioned.

The top product of the stripper 10 comprising HC1, H20 and H2804 is passed via a line 12 having a trap 14 therein to a mist eliminator 16. In the latter unit, substantially the last vestige of H2804 is removed. This aqueous acid, along with material derived from the trap 14, is conveyed to the bottoms line of the stripper 10 while the demisted aqueous HC1 vapors are introduced into a condenser 20.

To remove the excess chlorine, i.e., the chlorine not consumed in the oxidation of the S02 content of the feed liquid to H2804, the aqueous HC1 from the condenser 20 is passed through a bed of activated carbon 22. From the carbon bed, the essentially sulfur-free aqueous HC1 product, normally containing about 35 percent HC1, is led to storage.

The right-hand portion of the drawing has relation to the production of essentially sulfur-free anhydrous HC1 in accordance with the invention. It is contemplated that the material processed is derived from a system according with that above described except for the omission of the chlorine addition 11. In such case, the aqueous HC1 product (from the aqueous product storage tank) contains typically 300 parts per million of 802. Such liquor is passed along with elemental chlorine admitted from the tank 28 to a stripper 30. Here again, the chlorine is used in stoichiometrical excess vis-a-vis the 802 content of the feed.

The overhead of the stripper 30 is fed via line 32 to the condenser 20, while the bottom product containing typically 27 percent HC1, 73 percent H20 and .5 p.p.m. C12 is conveyed to a second stripper 34. From the latter there is derived as the bottom product an aqueous HC1 solution containing of the order of 2l percent HC1. Such solution is passed to the surge tank 9 from which the stripper 10 is supplied.

The overhead from the stripper 34 is conveyed via a line 36 to a condenser 38 which connects with a separator 40. The liquid therein separated is passed to the stripper 34 via a line 41, while the wet HC1 gas is conveyed to the bottom of a drying tower 42. Drying of the gas in such unit is accomplished with H2804 admitted from a stripper 44 served by an air blower 48. The function of the stripper 44, with blower 48, is to remove S02 from the H2804 derived from tank 46. By such means, the SO2 content of the H2804 is normally reduced to about l p.p.m. The residual C12 in the wet gas charged to the drying tower 42 is removed by reaction with the residual S02 in the H2804 from the stripper 44.

The substantially dried HC1 gas from unit 42 is passed through desiccating units 62 and 64 respectively containing, as the desiccants, aluminum Oxide and aluminum chloride. From the latter unit, the dry gas is conveyed via line 52 to a compressor 54, the output line of which leads to a storage tank 56.

The invention claimed is:

1. Method of producing essentially sulfur-free aqueous or anhydrous HC1 from an aqueous liquor containing HC1 and S02, said liquor being of industrial origin and containing the SO2 in minute concentration expressed in parts per million, said method comprising treating said liquor with elemental chlorine applied in stoichiometrical excess with respect to the 802 content of the liquor, said treatment resulting in the oxidation of the S02 to H2804, and subsequently removing such H2804 and the excess chlorine from the HC1 product.

2. Method of claim 1 where the aqueous liquor is derived by the absorption in water of the dedusted vapor eluent of a reactor applied to achieve the reaction:

3. Method according to either of the preceding claims Where the excess chlorine is removed by means of activated carbon.

4. Method according to either of claims 1 or 2 where the excess chlorine is consumed by reaction thereof with SO2 contained in H2804 employed in the drying of the HC1.

References Cited UNITED STATES PATENTS 804,515 11/1905 Askenasy et al. 23--154 XR 1,528,255 3/,1925 McKee 23-154 XR 1,781,830 11/1930 Barstow 23-154 XR 4 Burrage 23-154 Brown et al. 23-154 Herold et al. 23-154 XR Smith 23--154 Mohr 23-154 Latchum 23-154 Bottenberg et al. 23--154 Giraitis et al. 23--154 XR Brandmair et a1. 23-154 XR FOREIGN PATENTS Great Britain.

U.S. C1. X.R. 

